In a conventional Internet protocol (IP) multimedia subsystem (IMS), a proxy call session control function (P-CSCF), or edge proxy, can enable policy and charging to be implemented according to the session description protocol (SDP) and the presence and value of other session initiation protocol (SIP) headers. The SDP will typically be negotiated using SIP. Unfortunately, SIP headers can be manipulated in attempts to circumvent operator policies.
In addition, 3rd Generation Partnership Project (3GPP) security may be relatively complex and expensive, and other approaches include those that are relatively message intensive, or those not widely implemented. Furthermore, 3GPP IMS security does not prevent attacks from authentic IMS users. Thus, attacks on SIP infrastructure may be difficult to stop using conventional approaches. However, prevention of such attacks is desirable in order to preserve operator policies.